This invention relates to a stamping device particularly for providing holes in unfired ceramic substrates, also referred to hereafter as xe2x80x9cgreen sheetsxe2x80x9d.
In the manufacture of, for example, multilayer ceramic substrates used as circuit boards for supporting and electrically contacting electrical and electronic components, it is often required to provide a predetermined hole pattern in flat green sheets. The holes which may serve, for example, for a throughgoing contacting of printed circuit conductors, are provided by hole-stamping devices which, to ensure the required accuracy of the circuit board construction, are made with a tolerance of a few microns.
U.S. Pat. No. 5,233,895 discloses a stamping apparatus for stamping green sheets. The apparatus comprises an essentially stationary table on which the green sheet is positioned and on which it may be shifted as required. Above the table a base or carrier body is arranged which has a guiding device for an axially movable punch. The free end of the punch which serves as the stamping tool is axially displaceably supported in a throughgoing opening of an otherwise cup-shaped guide. In the table, facing the punch, an opening is provided into which the punch end may penetrate.
The punch is connected at its upper end with a cylindrical coil positioned in the annular gap of a permanent magnet arrangement in which a radial magnetic field is produced. An electrical energization of the coil thus results in an axial motion of the coil and the punch so that the latter may be moved into an advanced position and back into a retracted position.
The repeated stamping operations cause wear of the punches requiring their periodic replacement, either individually or as a group.
For performing such a replacement, U.S. Pat. No. 5,024,127 discloses the provision of a coupling device to releasably connect the electric drive arrangement and the stamping device formed by a punch. The punch is guided in a guiding device for axial displacements. The driving device has a plunger aligned with the punch and is movable by means of an electric drive connected with one end of the plunger. That end of the plunger which is oriented towards the punch and oriented away from the drive carries a coupling element which accommodates a head provided on the punch. For this purpose the coupling element defines a socket which, in the axial direction, is bordered by an engagement face for the frontal end of the punch and a second, split surface which is defined by a fork and which serves as an engagement face for the punch head. In case the driving device, the plunger and the coupling element are separated from the punch, the position of the punch is undefined. It may therefore move, for example, under its own weight, into a position which does not correspond to the position of disengagement. Such an occurrence may render the handling of the apparatus more difficult and may lead to problems particularly in case the punch has to be periodically replaced, for example, because of wear.
It is an object of the invention to provide an improved stamping device of the above-outlined type whose handling is rendered better compared to conventional devices, particularly in case of punch replacement.
This object and others to become apparent as the specification progresses, are accomplished by the invention, according to which, briefly stated, the stamping device includes a base body; an elongated punch having a longitudinal axis; a supporting arrangement for holding the punch in the base body and for guiding the punch for axial displacements between an advanced position and a retracted position; a driving unit releasably held in the base body and including a driving device for axially displacing the punch; a coupling device having a first state in which the coupling device operatively connects the driving device with the punch and a second state in which the driving device is disconnected from the punch; and a receiving arrangement for holding the punch in a desired axial position when the coupling device is in its second state.
Thus, the stamping device according to the invention has a base body on which one or a plurality of punches are axially shiftably supported between an advanced (stamping) position and a retracted position. The shifting of the punch is effected by a driving unit which has preferably a separate driving device for each punch. The driving devices are controlled by a control unit in such a manner that the punches may be shifted briefly into the stamping position to thus perform the stamping step. The transmission of the axial motion from the respective driving device to the associated punch is effected by a coupling device which may be disengaged when required. The coupling device provides for a fixed connection between the driving device and the respective punch in the axial direction and thus makes possible the axial transmission of motion, whereby the driving device determines the axial position of the punch. In case the driving device is separated (disconnected) from its associated punch, the axial position of the punch is no longer set by the driving device. For such a case, according to the invention, the receiving device serves to hold the punch in a desired axial position. The purpose of such a positioning is, for example, to prevent the punch from assuming unintentionally its advanced position in which its free end (stamping end) would project from its guide and from the base body and thus would be exposed to risks of being damaged. The receiving device sets the position of the respective punch at least to such an extent that its range of motion is significantly limited at least in one direction, while it may move freely in the opposite direction. Such an arrangement has, for example, the advantage that, after the driving unit has been removed, the punches may be taken out of their guide and may be replaced.
The receiving device which takes over the punch as long as the driving unit is disengaged, holds the punch in a predetermined position even when the driving unit is re-positioned or reconnected. Such steps may be particularly easily performed and thus a significantly simplified handling is achieved.
Preferably a plurality of identically structured punches are supported by the base body or, more precisely, by a guiding device supported on the base body, in such a manner that the punches are displaceable axially independently from and parallel to one another, provided they are released by the receiving device. In case the punches are received by the receiving device, they are all held in a predetermined position, preferably in the retracted position.
According to a preferred embodiment of the invention, the punches are each formed by a cylindrical shank adjoined, as the stamping tool, by a cylindrical stamping portion, whose diameter is significantly less than the diameter of the shank. The shank is supported in a guide, such as a guide sleeve. The stamping portion passes through an opening of a cup-shaped guiding or stripping element. In the withdrawn position the stamping portion does not project beyond the guiding and stripping element; the frontal end of the stamping portion is positioned within an opening provided in the guiding and stripping element. The shank and the stamping portion are preferably in a coaxial alignment with one another. The guide sleeve guides the shank during introduction of the punch with such an accuracy that the stamping portion penetrates into the opening of the guiding and stripping element without contacting or colliding with the latter.
At its end remote from the stamping element, the punch preferably has a head which, together with the coupling element associated therewith, forms the coupling device for coupling the punch to the driving device. The coupling element connects the punch in a form-fitting (form-locking) manner; for this purpose the coupling element has a laterally open socket for the punch head. The socket is bordered by two facing surfaces between which the head of the punch passes with a very small clearance or with practically no clearance. For uncoupling the driving device from the punch, the punch is laterally displaced relative to the driving device, so that the punch head may move out laterally from the socket. The coupling elements of all the driving devices or at least of one group of the driving devices are identically oriented so that the coupling and uncoupling of the coupling devices may be effected by a lateral displacement of the entire driving unit or a determined group of driving devices. As a result, it is, for example, feasible to remove a driving unit from the stamping device, whereby the punches separately driven by the respective driving unit are individually accessible and replaceable, if required.
As a receiving device for the punch heads a head plate is provided which is positioned between the driving unit and the guiding devices for the punches. The guiding devices are provided on the base body and are formed, for example, by guide sleeves. The head plate is thus situated in the vicinity of that end of the respective punch which is oriented towards the respective driving device and is thus in the vicinity of the coupling device. In such a position the head plate may take over the punches by their heads when they are released by the coupling elements. As the driving unit is disconnected from the punches, the latter are received by the head plate so that the punches may not move in an uncontrolled manner into an undesired position, for example, into an advanced (stamping) position.
For receiving the punch heads, a special engagement zone (punch head supporting surface region) is provided on the head plate preferably for each punch. The engagement zone is shifted underneath the punch head before the latter may entirely move out of the coupling element. Advantageously, the engagement zone formed on the head plate lies at the same level as the corresponding engagement face on the coupling element, that is, it is situated coplanar therewith, when the coupling element is in the retracted position.
In order to hold the coupling element positively in the retracted position during uncoupling, the coupling element preferably has an end face which, when the coupling element is in the retracted position, is situated at the same level as a supporting surface provided at the underside of the head plate. As result, during uncoupling, the coupling element is in a firm engagement, for example, with the base body or a counter support and is thus positively maintained in a position in which a transfer of the punch head from the socket to the head plate is feasible.
On the coupling element a positioning surface may be provided which adjoins the lower end face of the coupling element and which serves to guide the coupling element into a replacement position in which the punch head may be transferred to the head plate. Such a replacement position is preferably the position which determines the retracted position of the punch. The positioning surface may be formed, for example, by an oblique run-on face which may cooperate with a stationary edge (counter support) formed, for example, on the base body.